A plume of hexavalent chromium, a metal used in industrial production that the Centers for Disease Control and Prevention calls a "well-established carcinogen," has spread under Garfield, putting about one-tenth of the city's homes â¿¿ about 600 structures and 3,600 residents â¿¿ at risk.

The Environmental Protection Agency is about to start drilling on the spill site to determine how much chromium is pooled beneath and remove tainted soil. The agency is also testing the broader area to determine how it will be cleaned up. Now a group of scientists from New York University is working to assess how much chromium residents may have been exposed to.

Researchers will collect toenail clippings from city residents. The nails will be tested for traces of chromium. Because toenails grow slowly, it is possible to see how much chromium has accumulated in the body over the past 18 months or so, said Judith Zelikoff, a professor of environmental medicine at New York University.

"Our major goal is to try to relieve their fears," Zelikoff said. "With the economy, they can't sell their homes. They don't know if they got exposed."

The contamination started 30 years ago, when thousands of pounds of hexavalent chromiumâ¿¿ the same stuff that sickened Californians whose story was told in "Erin Brockovich" â¿¿ leaked from a tank at the EC Electroplating Co., a factory surrounded on all sides by houses and apartments. The state started cleaning up the spill but stopped two years later. In 1993, chromium was found at a now-shuttered firehouse and later in homes.